The chief objective of the proposed study is to continue anatomical research on the mammalian accessory optic system (AOS). To trace neurons, use will be made of the methods of anterograde transport of 3H-amino acids, retrograde transport of horseradish peroxidase (HRP) and double-label, retrograde transport of fluorescent tracers. The first phase of study revealed that the medial terminal nucleus (MTN) of the AOS projects strongly to brain stem nuclei involved with oculomotor function. In the proposed second phase of study, two main goals are: First, to provide a systematic analysis of the projections of: (1) of the dorsal and lateral terminal nuclei (DTN and LTN) of the AOS, (2) the important neuronal group intercalated among the axons of the superior fasciculus, posterior fibers (ISFp) of the AOS and (3) the physiologically defined, vertical eye and neck movement related midbrain nuclei shown in the present research to represent terminal nuclei of the MTN (viz. nuclei of the ventral tegmental area (VTA), the medial part of the deep mesencephalic nucleus (DMNm), the medial nucleus of the midbrain periaqueductal gray (PAGm) and the interstitial nucleus of Cajal (INC). Second, to analyze retinal and non-retinal afferent projections to the DTN, LTN and MTN. These two goals are to be reached by studying: (1) the projections of midbrain pretectal oculomotor areas through systematic charting of labeled neurons after HRP injections into the optic pretectum, superior colliculus, and major termini of the MTN; (2) the projections of the DTN, LTN and ISFp through analysis of silver grain distribution after 3H-amino acid injections into each of these three accessory optic components; (3) the axonal collaterization of MTN neurons innervating different sets of terminal nuclei through the use of double neuronal labeling with fluorescent dyes; (4) the afferent inputs to the DTN, LTN and MTN by mapping the labeled brain stem neurons after HRP injections into each terminal accessory optic nuclei; and (5) the retinal ganglion cells (RGC's) projecting to the DTN, LTN and MTN using the same experimental cases as for (4). Emphasis will be placed upon identifying RGC types involved, determining any contribution made to these projections by displaced ganglion cells, and showing the dendritic spread of labeled RGC's in sublaminae of the inner plexiform layer.